Look for the S&P/Case-Shiller index to post a year-over-year decline of 1% when the latest results are released Tuesday, according to estimates from Zillow.

That would be the smallest decline in two years, when a short-lived run-up in home prices evaporated after federal home-buyer tax credits expired. Prices have been in negative territory ever since, as housing markets have struggled with a surfeit of homes and anemic demand.

But price declines are easing — and several other indexes are now reporting year-over-year gains — as the supply of homes for sale has fallen sharply. Those inventory declines, coupled with a modest uptick in demand, have helped stabilize home prices.

The Case-Shiller index, along with two others, from CoreLogic and the Federal Housing Finance Agency, use what’s known as a “repeat-sales model,” which means they look only at how prices have changed for the same home over time.

This provides a more accurate home-price level than median home price data, which instead can capture a shift in the mix of homes being sold in one month versus another month.

Case-Shiller and FHFA also provide a seasonally adjusted index, which smooths out month-over-month changes that are often distorted by seasonal factors. More homes generally sell in April than, say, January, so it shouldn’t be surprising to see prices rise as sales pick up.

While Case-Shiller still reports seasonally adjusted figures, it issued an advisory two years ago saying that the adjustments were less reliable given greater variations on housing activity since the housing downturn had deepened.

Here’s a look at what other home-price indexes measure, and what they’ve shown in recent months.

S&P/Case-Shiller:

What the numbers show: S&P/Case-Shiller reported a 1.9% decline for April home prices from one year ago. Prices were up by 1.3% from March, though the increase was around 0.7% after adjusting for seasonal factors.

What the index measures: S&P/Case-Shiller covers just 20 of the nation’s largest metros. It is value weighted, meaning more expensive homes have a bigger impact on the home-price reading. New York and Los Angeles alone account for 35% of the composite-20 index, both because these cities are large and because home prices there are among the most expensive in the country, according to Jed Kolko, chief economist at real-estate website Trulia.

Case-Shiller is good for showing historical trends for home prices, but it shouldn’t be used as a real-time gauge of home prices, even though it’s often treated that way. It reports home sales with a two-month lag, so on Tuesday, for example, it will report on home prices from May. Case-Shiller also uses a three-month moving average, which means it includes all sales closed in March, April, and May. Deals that closed in May were negotiated before that, which means Tuesday’s report will reflect even older sales activity.

Federal Housing Finance Agency:

What the numbers show: The FHFA house price index reported that prices rose in May by 3.7% from one year ago. Prices were up by 0.8% from April on a seasonally adjusted basis.

What the index measures: The FHFA index covers all 50 states and the District of Columbia, with data from all metro areas that have at least 15,000 transactions over the past 10 years. (FHFA provides a thorough FAQ here). The index is unit weighted, meaning that high-priced and low-priced homes are treated equally. It is comprised of homes with loans backed by Fannie Mae and Freddie Mac, which means there were fewer subprime and other exotic mortgages, such as option adjustable-rate mortgages, that contributed to some of the most frothy price gains. This is one reason why FHFA shows that home prices are down by 17% over the last six years, compared to Case-Shiller, which shows a nearly 35% decline—even though both indexes started to decline around the same time.

CoreLogic:

What the numbers show: CoreLogic, a data firm, reported that prices rose by 2% in May from one year ago. On a month-over-month basis, prices rose by 1.8% from April. Those figures aren’t seasonally adjusted.

What the index measures: CoreLogic covers sales transactions from all 50 states and the District of Columbia, with data from 1,172 counties. Like the Case-Shiller index, the CoreLogic index is value weighted. It also includes a separate index of prices that excludes distressed sales such as foreclosures.

Zillow:

What the numbers show: Home values rose in June by 0.2% from one year earlier, the first year-over-year gain recorded by Zillow since October 2007.

What the index measures: The Zillow index is different from these other measures. It has a broad coverage area of more than 150 metro areas. Zillow uses a proprietary model that spits out estimates based on other sales prices for nearby homes, the size and physical attributes of a home, and past sales history and tax-assessment data. While individual estimates of a particular home have some margin of error, when those individual estimates are aggregated for a particular zip code, city, county, or state, the margin of error shrinks. (Zillow provides a deeper explanation here, and Mr. Kolko at Trulia did an analysis of these and other measures via CalculatedRisk).